A "linking lock" of Taiwan Utility Model patent application No. 75203820 laid open on Taiwan Patent Gazette of Sept. 21, 1988 issue, Pages 503, 504 with a publication No. 103863 disclosed a door lock provided with an upper thumbturn 21 for retracting an upper dead bolt and a lower knob 11 for retracting a lower latch for opening a door inside the door.
If the upper dead bolt is extended outwardly for closing or locking the door and upon a rotation of the inside lower knob 11 to rotate the lower driving plate 54, a H-shaped slide 53 will be biased and raised by the lower driving plate 54 to bias an upper driving plate 52 to retract the upper dead bolt for opening the door. This is quite important for simultaneously retracting the deadbolt and the latch for quickly opening a door especially for an emergency escape from a public building in case of a fire.
However, such a conventional door lock has the following drawbacks:
1. The H-shaped slide 53 is slidably moved in a guide casing 51 formed in a lock housing 3. For instance, for raising the H-shaped slide 53 for biasing the upper driving plate 52 for retracting the upper dead bolt as biased by the lower driving plate 54, the side "leg portions" of the H-shaped slide 53 may be frictionally resisted by two longitudinal side walls in the guide casing 51 to heavily retard the sliding movement of the slide 53, thereby delaying an emergency door opening operation.
2. The H-shaped slide 53 has a larger contact area frictionally contacting the inside surfaces of the guide casing 51 and will be frictionally held or obstructed within the casing 51 especially when contaminated or packed by dirts, dusts or pollutants in between the slide and the casing inside surface, influencing a smooth door opening operation.
3. The H-shaped slide 53 should be made to have a wider width in order to match with a larger radius of each driving plate 52, 54 to increase a force arm of a leverage of either driving plate (wheel) 52, 54 for a lighter rotation force of the knob 11 or thumbturn 21, thereby increasing the volume of the lock housing 3 and influencing its esthetic decorative effect.
The present inventor has found the drawbacks of the conventional door lock and invented the present door lock set with simpler construction but with a smooth operation.